The present invention relates to a device for separating and removing air or gas from fluids for intravenous infusion into a patient. Most particularly, the invention relates to a device for separating and removing air or gas from fluids processed through pressure infusion systems and fluid warming devices before parenteral infusion into a patient.
U.S. Pat. No. 4,298,358 shows a fluid filter which separates gas from liquid and vents the separated gas from the filter. The filter includes a vented housing through which the fluid stream passes. Liquid-wetting filter means carried in the housing in the path of the fluid stream permits the passage of liquid only. Gas separated from the fluid is vented through vent opening means which is covered by a liquid-repellent filter to permit the passage of gas only. An automatic pressure sensitive control means may be used to seal the vent opening means against the entry of ambient air but to automatically release separated gas from the filter. The liquid-repellent filter may be secured to the housing by a mechanical bond between the housing and a fibrous backing carried by the filter, or a continuous band of medical grade tape may be used to attach the filter to the housing.
U.S. Pat. No. 4,601,712 shows an improved conduit communicating between a pressurized source of solution and a partially filled reservoir associated with a drip chamber in a continuous-flush system. The conduit comprises a tube that is bent at approximately a 45 degree angle so that solution discharging from the conduit is diverted to impinge against the interior wall of the reservoir before interfacing with the solution accumulated therein. The arrangement reduces bubble formation normally associated with turbulent discharge flow during filling and flushing of the system.
The device shown in U.S. Pat. No. 4,601,712 works satisfactorily. The entrained bubbles of air or gas do come out of the fluid faster that with other drip chambers. However, the impingement of the fluid against the wall of the device, while alleged to reduce turbulence associated with turbulent discharge flow, still produces a level of turbulence which is felt to be unsatisfactory to those skilled in the art. In addition, the drip chamber disclosed has no vent, and thus there exists the need to turn the device over to vent it.
U.S. Pat. No. 4,900,308 shows an air elimination device which includes a plenum arranged to cause a reduction in flow velocity of a physiological fluid whereby air bubbles form and rise to the top of the plenum. A hydrophobic membrane covers the top of the plenum, and the pressure in the fluid is greater than that which is required to drive the released air through the membrane and into the atmosphere. The air which collects at the top of the plenum forms a protective surface on the bottom of the hydrophobic membrane to prevent its being clogged by cellular materials. A support stand engages the air eliminator to hold it in the desired orientation whereby the air bubbles form at the top of the plenum.
While the device disclosed works well enough in continuous use, it has been found by those skilled in the art that the device may not work well in intermittent flow conditions. This is due to repeated membrane exposure to blood products. This has been found to cause clogging because the bubble layer in the device does not stay in place once fluid flow stops. When this occurs, the membrane will be contacted by cellular products when flow resumes, and will become clogged.
U.S. Pat. No. 5,779,674 shows a fluid gas removal drip chamber for use for parenteral administration of fluids is disclosed. The drip chamber has a hydrophobic barrier which extends into the interior of the drip chamber. The hydrophobic barrier preferably comprises at least a portion of a three-dimensional surface. In one embodiment, an inlet port allows fluid to enter the drip chamber from the top so that the fluid falls through an air space formed in the top of the drip chamber. By shaping the inlet port so that droplets of fluid are formed, a health care professional can monitor the fluid drip rate. In another embodiment, the hydrophobic barrier is configured so that little or no air space exists at the top of the drip chamber. The drip chamber includes means for venting air that is separated from the fluid within the chamber and at the same time preventing air from entering the chamber through the venting means. For certain applications, the drip chamber is provided with a hydrophilic filter for filtering the fluid prior to exiting the drip chamber. This device works satisfactorily under continuous and intermittent flow conditions, but requires a complicated and expensive support for the hydrophobic barrier used therein, and thus, is not cost effective.
Pressure infusion systems may deliver fluid at a rate which is too fast for the body to adequately warm, thereby increasing the risk of hypothermia. Therefore, fluid warming devices may be connected to the pressure infusion system to warm the intravenous fluids to body temperature (about 37xc2x0 C.) before infusion into the patient. However, warming the fluid, among other things, may encourage any air or gas bubbles entrained, or within the system, to travel with the fluid. It is well understood in the art that air or gas bubbles should be prevented from entering into the blood stream of a patient. Air or gas which does enter a patient""s blood stream may result in an embolism.
In the prior art, there are a number of devices for removing air or gas bubbles from intravenous fluid. One category of such devices is the drip chamber. In the drip chamber, the bubbles and the fluid are separated by dripping the fluid onto a fluid-gas interface. Gas is trapped in an unvented reservoir while the fluid is allowed to exit the reservoir. Traditionally, drip chamber devices are not well-suited for high fluid flow applications due to their limited volumetric capacity and due to excessive gas bubble creation at the fluid-gas interface. Often, the resulting excessive bubbles are not retained in the reservoir, but instead are allowed to escape through the outlet. Further, because of its limited volumetric capacity, a drip chamber is limited in the amount of air that can be processed, and must be inverted periodically to vent the air removed.
A second category of fluid-gas separation devices is a filter where the fluid passes through a filter medium that positively stops the passage of bubbles. Such filter mediums, however, may impede the flow of certain fluids through the device, including drugs being administered. Filter media are also prone to blockages that may result in a complete stoppage of fluid flow. Furthermore, when filter media are used for blood or blood products the fragility of the cells may limit the range of operating conditions of the device.
A third category of fluid-gas separation devices employs a hydrophobic barrier to allow air or gas within the fluid to pass through the barrier and escape to a vent. Although the barrier allows air or gas within a liquid to escape, the barrier prevents the liquid itself from escaping. Further, when the hydrophobic barrier is in the form of a tube, such as in the aforementioned U.S. Pat. No. 5,779,673, such fluid-gas separation devices are not cost effective.
Thus, none of the above-described devices are entirely suitable for high volume, high flow separation of air or gas from biological fluids such as saline, air, or blood on a continuous basis, such as is required by modern pressure infusion systems. It was desired, for example, to develop a device capable of venting a single 2 ml air bolus while infusing 20 ml of fluid As discussed above, the devices presently available can not do this on a continuous basis, or can not do so without developing serious operational problems. Thus, those skilled in the art continued to search for a satisfactory high flow separation device.
The present invention provides an effective, low cost device for removing air or gas bubbles from fluids prior to intravenous infusion into a patient. The invention is particularly well-suited for intermittent, or continuous gas bubble separation from solutions such as blood, blood products, saline or other biological fluids. The present invention is especially suitable for use at high fluid flow rates, where endurance and large venting capability is desired, such as during surgery, where the high flow separation device of the present invention may be used on a continuous or intermittent basis for up to four hours, or up to ten (10) units of blood. Additionally, the present invention has few parts, is easily manufactured and assembled, has exceptional durability when exposed to cellular components, and is low in cost when compared to existing devices.
The invention is a device for removing gas or air from fluids used in fluid warming devices before intravenous delivery to a patient. Fluid enters the device through at least one inlet. At least one passage directs the fluid from the inlet into a first chamber.
Fluid enters the chamber along the sidewalls thereof to create a smooth entrance into the chamber. It is desired that the fluid being processed does not xe2x80x9csplashxe2x80x9d into the chamber, but remains attached to, or reattaches itself to the sidewalls as it enters the first chamber. The smooth entrance of the fluid into the chamber also helps to create a fluid dead zone adjacent the porous barrier which assists the coalesced air or gas to pass through the barrier into second chamber.
The fluid xe2x80x9cdead zonexe2x80x9d is a zone within the first chamber where the fluid velocity is minimal or substantially non existent. There is no downward force on the gas bubbles, and the bubbles quickly rise and coalesce. This results in a more effective and expedited removal of any entrained gas. This, in turn, results in a substantially smaller housing design.
A plurality of interconnected channels within the second chamber collects and transports the air or gas to a vent. Gas re-introduction into the invention is prevented by locating a check valve downstream of the vent. Additionally, the outlet may be sized such than an appropriate back-pressure is created to prevent gas re-introduction into the device. In addition to the first chamber barrier, a porous barrier, preferably hydrophillic, may also be placed in the chamber upstream of the outlet to prevent the inadvertent passage of minor gas bubbles through the exit. If desired, such a barrier may be liquid wetting, and of an appropriate pore size to provide an automatic shut off if more air enters the system than desired. A clip, or similar means, may be used to secure the device to medical equipment adjacent the patient or fluid source.